In my aforementioned copending application I have disclosed an improvement in a bag-type filtering apparatus which provides significantly more effective cleaning of the filter bags when the bags are periodically backflushed by a reverse purge of air. As disclosed in the aforementioned copending application, means is provided extending longitudinally within the filter bag for diffusing and distributing air throughout the filter bag when a periodic reverse purge of air is directed into the filter bag. More particularly, a hollow diffuser tube is positioned within the filter bag, with the diffuser tube having perforations therein located for diffusing and distributing air throughout the filter bag when a periodic reverse purge of air is directed into the filter bag and into the diffuser tube. This arrangement prevents the otherwise concentration of the reverse purge of air in localized areas of the filter bag resulting in uneven and inefficient cleaning of the filter bag. The more uniform distribution of the purge of air throughout the filter bag achieves considerably more effective cleaning of the filter bag than has heretofore been possible in a conventional bag-type filtering system.
The present invention discloses an arrangement in which a diffuser tube of the type disclosed in my aforementioned copending application is employed in a particular type of filtering apparatus to obtain more effective utilization of the periodic reverse purges of air and to thereby obtain improved and more effective cleaning of the filter bags.
There are a variety of different types of filtering systems which employ tubular filter bags. In the particular type of filtering apparatus with which the present invention is concerned, a group of tubular filter bags are mounted in a filter housing or "baghouse" with each filter bag being supported in open hollow tubular configuration. Particulate-laden gas is directed into the filter housing and flows through the gas permeable filter bags while the particulate material is filtered and retained on the exterior surface of the filter bags. Periodically, the filter bags are cleaned by directing compressed air into the tubular filter bags to thereby flex or move the filter bags and dislodge the trapped particulate material from the exterior surface of the filter bags. The compressed air is directed into the filter bags as a high velocity jet pulse of compressed air from a pipe located outside of the filter bag and in axial alignment with the open outlet end thereof. The jet pulse of compressed air is intended to sweep longitudinally along the interior of the filter bag from the open outlet end to the closed opposite end thereof in a wavelike fashion causing a momentary expansion or flexing of the filter bag for dislodging the accumulated particulate material from the exterior of the filter bag. This type of filter bag cleaning arrangement is shown by way of example in prior U.S. Pat. Nos. 3,535,852; 4,073,632 and 4,157,901.
One of the problems with this type filtering apparatus is that the above-noted type of jet pulse cleaning arrangement is not very effective in removing the particulate material from the filter bags. After the filter bags have been in use for a period of time they become increasingly clogged with particulate material. This undesirably increases the pressure drop across the filtering apparatus and significantly reduces its efficiency.
Attempts have been made to increase the effectiveness of the jet pulse of compressed air in this prior type of filter bag cleaning arrangement by installing a venturi nozzle adjacent the open outlet end of the filter. The venturi nozzle is intended to increase the effect of the jet pulse of air to enable it to reach the full length of the filter bag. However, these attempts have not been fully effective in overcoming the problem of inadequate cleaning of the filter bag. It has been observed that in filtering systms utilizing the above-noted type of jet pulse cleaning arrangement, the filter bags are cleaned fairly well at the upper end thereof adjacent where the jet pusle of air enters the filter bag, but very little cleaning of the filter bag takes place at the lower end of the filter bag. Apparently, the pulse or jet of compressed air is substantially dissipated by the time it reaches the far end of the filter bag. Thus in this type of cleaning arrangement, the entire length of the filter bag has not been effectively utilized for filtration and the efficiency of the filter bag has been reduced accordingly.